Anyone with normal color vision agrees that blood is roughly the same color as strawberries, cardinals and the planet Mars. That is, they're all red. But could it be that what you call "red" is someone else's "blue"? Could people's color wheels be rotated with respect to one another's?

Well, all our shared models of reality are built on consensus; colour naming is just one small example. There is, after all, no such thing as blue or red or green, only different wavelengths. It's all perception of reality, not reality.

Even the statement about wavelengths cannot really be proven one way or another as all of science - or indeed any conceptual model - can always be argued against using Munchausen's trilemma. It's a cheap debating trick to do so in some ways, of course, but that's only because it's exceptionally hard to refute.

William James came up with a cute way to lever oneself off the horns of the trilemma which runs something along the lines of, "The philosopher achieves mental tranquillity in much the same way as the fool; they only differ as to the point at which they refuse to let fresh data impinge upon their absolute assumptions". In other words, everybody in the end simply chooses a model of reality which complements their psychological needs.

Thought some of you might find this interesting:
Anyone with normal color vision agrees that blood is roughly the same color as strawberries, cardinals and the planet Mars. That is, they're all red. But could it be that what you call "red" is someone else's "blue"? Could people's color wheels be rotated with respect to one another's?

This is hardly a new idea; you've never once pondered this previous to reading this blog post?

Not in my reading of it. Color blindness involves the inability of differentiating wavelengths at "green" levels from wavelengths at "red" levels.

Private color perception would entail everyone being able to differentiate between the different wavelengths - we all agree that the sky is "blue", strawberries are "red" - but our mental representations of these colors are different.

HF, I may be misreading you, but the idea here is different than the one you propose. It's not that the mapping from wavelengths to names of colors is arbitrary - this much is entirely clear. It's not that my reality is totally different from your reality. We all agree what is "blue". We agree that the sky and the sea and blue M&Ms are roughly the same color, just like roses and blood and the ties that Manton hates are all the same color. There's nothing necessarily "sociological" about this. It's a question of perception technology that we can identify the wavelength of light.

But my interior mental image may represent light at these wavelengths with a different representation than yours. It would seem very difficult to ever actually have any definitive proof of this being the case or not.

This isn't exactly a case of an inverted (or rotated) spectrum, but there may be some people who can discriminate between more colors than the average person, in the way that some birds and insects can. Look up "tetrachromacy." As Holdfast points out, the colors we experience aren't "there" in the world, they're a function of our perceptual apparatus. Anything with a different apparatus may well experience things differently.

As to whether these experiences are necessarily private, and if so what we should think about that, I leave that to Wittgenstein.

HF, I may be misreading you, but the idea here is different than the one you propose. It's not that the mapping from wavelengths to names of colors is arbitrary - this much is entirely clear. It's not that my reality is totally different from your reality. We all agree what is "blue". We agree that the sky and the sea and blue M&Ms are roughly the same color, just like roses and blood and the ties that Manton hates are all the same color. There's nothing necessarily "sociological" about this. It's a question of perception technology that we can identify the wavelength of light.

But my interior mental image may represent light at these wavelengths with a different representation than yours. It would seem very difficult to ever actually have any definitive proof of this being the case or not.

My post directly addresses that precise idea. That's why we have developed a consensus model of reality whereby we can all agree what blue is, regardless of what we actually perceive as blue. That's the only reason my reality is not totally different to your reality. In theory/isolation, it really IS (paceGattopardo above, and indeed, Wittgenstein ). In practice/culture, we agree on a model that maps our perceptions to equivalent phenomena. We wouldn't even agree on what blue is without that shared concept (?delusion). It's not a new idea (it's just a perceptual spin on "what is truth" and idealism generally), though we are increasingly able to practically identify mechanisms and illustrations for our individual perceptual differences.

I blogged about this issue a week or so ago, when asking the question "what does Coke taste of"? We all perceive the taste of Coke differently/individually, but we also all agree to call it Coke. It's another example of this consensual model of reality that isn't just based on our perceptions, but on how we compare our perceptions to others. That lets us "calibrate" our terminology to mean the same thing, regardless of what we actually perceive neurochemically. If you think about it, given genetic variation and synaptic plasticity, it would be staggeringly, staggeringly UNlikely for us all to perceive a given physical phenomenon in the same way. We just agree on how to describe it.

And even then, not always, when the differences become increasingly marginal. For instance, there's a tribe in the (I think) Amazon that literally can see more shades of green than the rest of us. Because of this, combined with their relative isolation to the rest of the world, they can describe more greens than us. They have both a perceptual ability that we lack AND a different nomenclature to accompany that difference. If you took someone from that tribe and raised them in OUR culture, without exposure to their own, the chances are very high that while they'd continue to see all those extra differences if you tested them, in practice they'd only call them by the shades that the rest of us can name, as they'd be embedded in our version of reality.

My post directly addresses that precise idea. That's why we have developed a consensus model of reality whereby we can all agree what blue is, regardless of what we actually perceive as blue. That's the only reason my reality is not totally different to your reality. In theory/isolation, it really IS (paceGattopardo above, and indeed, Wittgenstein ). In practice/culture, we agree on a model that maps our perceptions to equivalent phenomena. We wouldn't even agree on what blue is without that shared concept (?delusion). It's not a new idea (it's just a perceptual spin on "what is truth" and idealism generally), though we are increasingly able to practically identify mechanisms and illustrations for our individual perceptual differences.

I blogged about this issue a week or so ago, when asking the question "what does Coke taste of"? We all perceive the taste of Coke differently/individually, but we also all agree to call it Coke. It's another example of this consensual model of reality that isn't just based on our perceptions, but on how we compare our perceptions to others. That lets us "calibrate" our terminology to mean the same thing, regardless of what we actually perceive neurochemically. If you think about it, given genetic variation and synaptic plasticity, it would be staggeringly, staggeringly UNlikely for us all to perceive a given physical phenomenon in the same way. We just agree on how to describe it.

And even then, not always, when the differences become increasingly marginal. For instance, there's a tribe in the (I think) Amazon that literally can see more shades of green than the rest of us. Because of this, combined with their relative isolation to the rest of the world, they can describe more greens than us. They have both a perceptual ability that we lack AND a different nomenclature to accompany that difference. If you took someone from that tribe and raised them in OUR culture, without exposure to their own, the chances are very high that while they'd continue to see all those extra differences if you tested them, in practice they'd only call them by the shades that the rest of us can name, as they'd be embedded in our version of reality.

OK, I understand you better now - and thanks for the link to your blog post. We are talking about the same thing. I'd hesitate to say that the Amazonian living in the West would be "embedded in our version of reality" as they CAN still see the different shades of green. They may not realize that others can't see them, but in this case, there would be an obvious way to test whether this is true. With reference to the open of your blog post, I do prefer "the real would drive us mad" to "there is no real". I'm not sure how far you mean to take this "version of reality/positive consensus taste construct", but the fact that we all agree on which things are "blue" is not a social construct in the same way as we agree on which things are "fair". "Blue" has a definite meaning, which is things that reflect light of a certain frequency. "Fair", or its translations in other languages, can mean different things in different societies, and is agreed upon less often by different people even within the same culture. If I were to meet a person who lived in the Amazon for their entire life without contact with Western culture, and told him, "this thing is blue - everything of this color, we call blue", he would know exactly what I mean and call all the same things blue that I would call blue. If I told him, for instance, "I entered the lottery and won, so now I am very rich and get to spend a lot of money. It's fair, because everybody who entered had the same chance of winning." He might have no idea what I mean and think that it couldn't possibly be fair for one person to end up with so much money and everyone else so little, and if he learned the meaning of the word, we might call very different things "fair".

Thought some of you might find this interesting:
Anyone with normal color vision agrees that blood is roughly the same color as strawberries, cardinals and the planet Mars. That is, they're all red. But could it be that what you call "red" is someone else's "blue"? Could people's color wheels be rotated with respect to one another's?
entire article here:http://www.lifeslittlemysteries.com/2612-color-red-blue-scientists.html

The concept of Qualia - Much ink has been spent on this topic for oh, at least 5000 years since writing was invented and probably since before that. Read a short intro on wiki.